In recent years, cases in which images that are used for a presentation or the like are projected from a projector to a projection object such as a screen and in which they are shared by many people have been increasing.
A projector is a device that displays an image on a projection object by causing light projected from the projector to be diffused and reflected on the projection object. In this case, luminance that is apparent brightness of a projection image displayed on the projection object varies depending on the intensity of light projected from the projector. This intensity ordinarily depends on the output value of a light source lamp with which the projector is provided.
The output intensity of this light source lamp with which each projector is provided ordinarily has been designated like 220 W, 300 W, etc. Thus, the luminance of a projection image largely varies depending on the environment where the projector is used, for example, the projection distance between the projector and the projection object, the zoom ratio, and so forth. For example, the shorter the distance between the projector and the projection object, the higher the luminance of the projection image becomes, whereas the smaller the zoom ratio, the higher the luminance of the projection image becomes.
In this way, there are situations in which the luminance of a projection image varies depending on the environment where the projector is used, resulting in situation in which the luminance of a projection image became excessively high or excessively low.
Thus, there is demand for a technique that allows the luminance of a projection image to become constant regardless of the environment where the projector is used and one related art reference has been disclosed for example in JP 2003-241311A.
In the technique disclosed in JP 2003-241311A, the intensity of light projected from a projector is adjusted depending on the projection distance between the projector and the projection object and a zoom ratio, such that the luminance of the projection image can be prevented from becoming excessively high or excessively low regardless of the environment where the projector is used.
Besides the projection distance and zoom ratio, the luminance of a projection image varies with the reflectance of the projection object.
Since the reflectance of the projection object varies depending on the type and color of the projection object, when the type and color of the projection object are different, the problem in which the luminance of a projection image cannot be kept constant arises.